The new front-end engineering and design work and updated definitive feasibility study outlines a higher US$182 million capital cost for the 1.15 million tonne per annum module one that will produce 89,000t of graphite concentrate.
The capex has increased from the $116 million expected in 2019 due to global inflationary pressures, plus optimisation and debottlenecking improvements that should deliver a more flexible plant.
Mahenge is ultimately designed as a four-module operation processing 4Mtpa of open pit ore to produce 347,000tpa at steady state.
The studies show it should have average C1 cash costs over the first decade of $466/t, compared with consensus pricing of $1709/t.
That delivers the company a lower post-tax net present value and internal rate of return of $1.4 billion and 36% respectively than expected in 2019. Payback is 3.8 years.
However, running the numbers using just FastMarket's more bullish pricing assumption of $2563/t doubles NPV and slashes payback to 2.7 years, boosting IRR to 55%.
The work, completed with its construction contractor CPC Engineering, will now be used to lock in finance term sheets.
A second module, which could be developed in tandem with stage one, could cost $107 million and would be largely funded by US-based Urbix.
It would not change Black Rock's equity requirements and would allow it to double capacity into what could be a market demanding more graphite.
Black Rock is also examining fast tracking a $33 million power connection to nearby hydro electricity generation earlier than originally planned due to much higher diesel costs.
If developed, it will deliver products that have some of the lowest carbon emissions in the world.
Black Rock CEO John de Vries said the updated studies showed a project with "outstanding" returns.
The company hopes to have its financing locked before the end of the year.
It last raised A$25 million at 24c per share earlier this year.
Black Rock will own 84% of the project, carrying Tanzania's government's 16% share.
Construction now is expected to take around two years.
Black Rock shares, which have traded at A13c-33c over the past year were last traded at 19c, valuing the company at $191 million.
